1. Field of the Invention
This invention relates to an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus and a cartridge mountable on this apparatus, and particularly to an image forming apparatus having a mechanism for detecting the amount of developer residual in a developing device, and a cartridge.
2. Related Background Art
In an image forming apparatus using the electrophotographic image forming process, there has heretofore been adopted a process cartridge system in which an electrophotographic photosensitive member and process means acting on the electrophotographic photosensitive member are integrally made into a cartridge which is removably mountable on the main body of the image forming apparatus. According to this process cartridge system, the maintenance of the apparatus can be done by a user himself without a serviceman being resorted to and therefore, operability could be markedly improved. So, this process cartridge system is widely used in image forming apparatuses.
In an image forming apparatus of such a cartridge type, the user himself interchanges the cartridge and therefore, means for informing the user when the toner has been consumed or when the life of a photosensitive drum which is an electrophotographic photosensitive member has completed its span.
So, there has been proposed a method of integrating and memorizing the amount of use of the cartridge by utilizing non-volatile memory means such as EEPROM as means for detecting the lives of parts and the amount of consumed toner. For example, Japanese Patent Laid-Open Application No. 61-185761 describes an image forming apparatus provided with means for adding and memorizing the information of the exposure time when a photosensitive drum in a process cartridge is exposed to a laser beam or a light emitting diode, i.e., information corresponding to the amount of remaining toner.
Also, such a process cartridge is frequently mounted and dismounted with respect to an apparatus body and therefore, it has also been proposed to contain memory means in the cartridge itself, and enhance the detection accuracy when for example, a plurality of cartridges are used for an apparatus body. For example, Japanese Patent Laid-Open Application No. 63-212956 proposes an electrophotographic recording apparatus in which a memory is provided within a cartridge and means for effecting the reading-out/writing-in of the memory is provided in the apparatus body and the calculation of information regarding the life of the cartridge is effected on the basis of the content read out from the memory and the electrophotographic operation and the information is written into the memory.
Also, Japanese Patent Laid-Open Application No. 3-230172 proposes an image forming apparatus in which a non-volatile memory medium provided in an interchangeable unit is caused to memorize the information of the characteristic of the unit and the amount by which the unit has been used.
Also, as another method of detecting the time of interchange of a cartridge, there has been proposed a method of directly detecting the amount of toner remaining in a cartridge, and informing the user when the amount of remaining toner has become a predetermined value or less, to thereby call upon the user to interchange the cartridge. For example, Japanese Patent Laid-Open Application No. 62-62352 describes a method of disposing an antenna for detecting the amount of residual toner near a developing roller which is a developer carrying member, measuring an electric current induced in the antenna when an AC voltage is applied to the developing roller, and detecting the amount of residual toner by utilizing the fact that it changes in conformity with the amount of toner between the developing roller and the antenna.
However, the method of detecting the amount of residual toner by the change in the electrostatic capacity between the sleeve and the antenna described in Japanese Patent Laid-Open Application No. 62-62352 has suffered from the following inconveniences. Since the above-described means is one for detecting a delicate change in the electrostatic capacity between the sleeve and the antenna, it is desirable that the distance between the sleeve and the antenna be free of any individual difference and be constant. However, a dimensional tolerance always occurs in manufacture and therefore, the distance between the sleeve and the antenna cannot always be said to be as per the design value. Also, the antenna bar used is often as small as possible in its diameter in order not to hamper the movement of a toner in a developer container 6 and therefore, when mounted on an image forming apparatus, the antenna bar becomes liable to flex in its lengthwise direction. Thus, the distance between the sleeve and the antenna becomes long in some portion and short in some portion and disorder occurs to the delicate change in the electrostatic capacity.